Principles of Food Canning
Food and Agriculture Organization of the United States—Food and Sterilization Procedures states that unlike pasteurized “cooked” meat products where the survival of heat resistant microorganisms is accepted, the aim of sterilization of meat products is the destruction of all contaminating bacteria including their spores. Heat treatment of such products must be intensive enough to inactivate/kill the most heat resistant bacterial microorganisms, which are the spores of Bacillus and Clostridium. In practice, the meat products filled in sealed containers are exposed to temperatures above 100° C. in pressure cookers. Temperatures above 100° C., usually ranging from 110-121° C. depending on the type of product, must be reached inside the product. Products are kept for a defined period of time at temperature levels required for the sterilization depending on type of product and size of container.
If spores are not completely inactivated in canned goods, vegetative microorganisms will grow from the spores as soon as conditions are favorable again. In the case of heat treated processed meat, favorable conditions will exist when the heat treatment is completed and the products are stored under ambient temperatures. The surviving microorganisms can either spoil preserved meat products or produce toxins which cause food poisoning of consumers.
In embodiments herein only fully sterilized meat products, which can be stored under ambient temperatures, are considered. So called semi- or three-quarter sterilized products, which require lower than ambient storage temperatures, are not considered as they are not particularly well suited for developing countries.
Amongst the two groups of spore producing microorganisms, Clostridium is more heat resistant than Bacillus. Temperatures of 110° C. will kill most Bacillus spores within a short time. In the case of Clostridium temperatures of up to 121° C. are needed to kill the spores within a relatively short time.
The above sterilization temperatures are needed for short-term inactivation (within a few seconds) of spores of Bacillus or Clostridium. These spores can also be killed at slightly lower temperatures, but longer heat treatment periods must be applied in such cases to arrive at the same level of heat treatment.
From the microbial point of view, it would be ideal to employ very intensive heat treatment which would eliminate the risk of any surviving microorganisms. However, most canned meat products cannot be submitted to such intensive heat stress without suffering degradation of their sensory quality such as very soft texture, jelly and fat separation, discoloration, undesirable heat treatment taste and loss of nutritional value (destruction of vitamins and protein components).
In order to comply with above aspects, a compromise has to be reached in order to keep the heat sterilization intensive enough for the microbiological safety of the products and as moderate as possible for product quality reasons.
A method was developed for such a balance between food safety and food quality requirements by measuring and quantifying the summary amount of heat treatment to which a canned product is exposed during the entire sterilization process.
Meat Products Suitable for Canning
Practically all processed meat products which require heat treatment during preparation for consumption are suitable for heat preservation. Meat products which do not receive any form of heat treatment before being consumed, such as dried meat, raw hams or dry sausages, are naturally not suitable for canning as they are preserved by low pH and/or low water activity.
The following groups of meat products are frequently manufactured as canned products:                cooked hams or pork shoulders        sausages with brine of the frankfurter type        sausage mix of the bologna or liver sausage type        meat preparations such as corned beef, chopped pork        ready-to-eat dishes with meat ingredients such as beef in gravy, chicken with rice soups with meat ingredients such as chicken soup, oxtail soupCan Linings        
Metal food and beverage cans have lining on the interior surface, which is essential to prevent corrosion of the can and contamination of food and beverages with dissolved metals. In addition, the coating helps to prevent canned foods from becoming tainted or spoiled by bacterial contamination. The major types of interior can coating are made from epoxy resins, which have achieved wide acceptance for use as protective coatings because of their exceptional combination of toughness, adhesion, formability and chemical resistance. Such coatings are essentially inert and have been used for over 40 years. In addition to protecting contents from spoilage, these coatings make it possible for food products to maintain their quality and taste, while extending shelf life.
However, these epoxies contain a chemical called BPA or bisphenol A. which has faced much scrutiny from consumer advocacy groups. California proposed, for the second time, to list bisphenol A as a cause of reproductive toxicity under a state law called Proposition 65. Although the maximum allowable dose would be too high to require warning labels on most products, such as food cans that are lined with BPA-based epoxy resins, the proposal adds another reason that people might want to avoid the chemical.
In the past decade, consumers and health experts have raised concerns about the use of BPA in food packaging. The molecule has a shape similar to estrogen's and thus may act as an endocrine disrupter. The chemical industry and makers of metal food packaging contend that BPA is safe.
But for food companies, pleasing consumers is a high priority, and most are eager to move away from packaging based on BPA. Coating manufacturers and their suppliers are working overtime to find a replacement for the ubiquitous epoxies, which are made by reacting BPA with epichlorohydrin.
Heat sealable polyester film is one solution to replacing cans lined with an epoxy coating. Biaxially oriented polyester (BOPET) films are used for multiple applications such as food packaging, decorative, and label for example.
The food packaging industry commonly use BOPET films in many heat sealable tray applications where direct contact of food to BOPET is common, to take advantage of the intrinsic properties of BOPET such as clarity and tensile strength and its' inert chemical composition.